How to measure room pressures

Other then complying with SWS 6.6201.3a (No room will exceed +/- 3 pascals with reference to the outside with all interior doors closed and ventilation systems running) is anyone measuring room pressures, and if so, are you measuring the pressure in the room WRT the main body or to the outside? With all interior doors closed or closing one door at a time?

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Since the specification you are quoting (?) specifies ventilation system and all interior doors closed and with reference to outside, one can would deduce it is there to test for an imbalance in flows from the ventilation system. If it across the inside doors it would be testing for unbalanced flows to the room (from the ventilation system). If the ventilation system is locked into the HVAC system (such as the much hated duct from outdoors to the return plenum) then the HVAC system should run at it's normal operating speed.

In essence without knowing what the heck this was meant to test it appears to be superfluous or possibly absurd.

Edited to add - The 3Pa has been a part of the local Green Building Program requirements for years. It was to make sure any pressure difference created by closing interior doors was too low to backdraft a combustion appliance. So you would want to create the worst case conditions (all interior doors closed, highest operating fan speed and measure to the outdoors). Once the test is setup (close doors & turn on fan) you would measure one room at a time but leave all doors closed.

I recall old instructions that said something about using a smoke puffer to determine if a door should be open or closed during this test. Maybe John Proctor or someone would like to comment.

We test for the Weatherization Assistance Program. But the Standard Work Specifications and the BPI 1200 -s-2017 no longer require or mention testing room pressures except for SWS 6.6201.3a (No room will exceed +/- 3 pascals with reference to the outside with all interior doors closed and ventilation systems running).

If you are going for just a good system I would stick w the 3pascal limit and would aim for less. Any air not returning to the system from each room will be gained from elsewhere. Most likely outside air, adding load as well. Personally I would test with all doors closed in cooling mode as a worst case scenario.

Daniel wrote: "Any air not returning to the system from each room will be gained from elsewhere."

Not necessarily. Notwithstanding combustion safety testing (which predates green building programs), zonal pressure testing is an important (I would say necessary) verification step to ensure adequate return pathways exist for forced air heating and/or cooling distribution. In situations where you don't have adequate return paths, a closed door not only reduces airflow to the now isolated room but can cause system airflow to drop as well instead of being pulled from other rooms.

The Weatherization Assistance Program Standard Work Specifications vary state to state. I suggest contacting your state office for clarification. I would want to know how they define ventilation systems. Does this include exhaust fans, supply fans, HRV and ERVs, the air handler? At what speed should the air handler be running?

If the measured House / Outside pressure exceeds the stated limit, you would need further diagnostics to determine the dominant door. To determine the dominant door, turn on ventilation systems and check door pressures one at a time starting with all doors open. Measure the room / hall pressure. The door that you have to open the most to relieve the pressure to 3 Pascals is the dominant door. Start by treating that door first.

Next time you final a new house or complete a home energy audit: Tape off the return in one bedroom. Then turn turn AH on - heat or cool. Now place the manual damper (*aka door") to about 4 inches from closed. After it closes think about a toddler or a grandparent not moving their fingers fast enough.

Now remove open half the return and repeat. Then open fully and repeat. You can even measure the Pressure across the damper.

I have used this to demonstrate an undersized duct.system.

If you have to meet specific program requirements, those have to be met. In addition to this being a comfort issue, I see it as a safety issue.